Smart drill, jig, and method of orthopedic surgery

ABSTRACT

The present invention provides a MEMS sensor guidance system mounted on a surgical instrument and uses the MEMS sensor to determine Inertial Measurement Units to track rotation and acceleration in all three spatial directions. Further the invention provides a method of surgery in which a reference axis, a loci, and a depth are defined and the instrument including the sensor duster of the invention is placed in relation to the y-axis and x-axis and following the working end is aligned and the orientation and depth data display is observed to aid in maintaining the desired instrument.

FIELD OF THE INVENTION

This present invention relates to a surgical instrument, which uses anovel surgical guidance system including a microprocessor having memoryloaded with appropriate software and one or more sensors in order totrack and/or recommend the orientation and movement over time of a workpiece or implant in a surgical field using a locally defined coordinatesystem such that the surgical guidance system provide surgicalassistance by means of a specifically designed graphical user interfaceon an associated display, to a surgeon at a economically efficient cost.The invention further relates to a method of surgery that uses thisinstrument and may include information stored in the system memory basedon generalized information, such as the location of openings in implantsor preferred angles for insertion or incision, or on information whichis specific to particular patient anatomy or surgical need. In a furtherembodiment, the invention relates to an aid or jig that is used todefine the local coordinate system.

BACKGROUND OF THE INVENTION

Surgeons, and in particular orthopedic surgeons have become accustomedto the use during surgery of mechanical devices, which act to aid thesurgeons in their work. Such devices include, for example, depth anddrill guides, and jigs, which help the surgeon to align fasteners withbone and with openings in implants so as to provide for the optimalalignment in the bone/implant/fastener construct. This is particularlyimportant in instances where fastener seats first in the bone, and thenlocks, such as through a threaded relationship with the implant.

Recent developments in surgery recognize the advantage of a surgicalapproach, which is less invasive than previous techniques, whichrequired relatively large incisions to provide open access to theultimate surgical field or work site. These relatively new “minimallyinvasive” procedures work through small incisions, and may even call forprocedures to be performed percutaneously, or through the skin. Suchapproaches provide less insult to the surgical environment, andtherefore result in shorter healing times, and ultimately bettersurgical outcomes. However, they also result in a more limited surgicalvisibility of the area where the surgeon may be developing a constructincluding for example, the bone, fasteners, and an implant.Consequently, device developers have designed mechanical means, such asjigs and guides, which help to locate components of the construct duringsurgical implantation (for example by providing a template for theimplant system) in a minimally invasive procedure, including relatedfasteners or surgical aids such as k-wires. While these means do provideadditional guidance, they tend to be awkward to use, and to obscure thesurgical view in their own way. Moreover, they are limited to aparticular placement and orientation, and do not assist in the variablelocation in space over time of a component of the construct (forexample, they can not account for the reduction of a bone fragment whichmay change the desirable location of a fastener within that bonefragment.)

Partly in response to trends in surgery realizing the value ofelectronic assistance, and partly as hardware and software systems havedeveloped to provide medical applications and increased accessibility,surgical navigation systems and robotic devices have been developed toprovide increased electro/mechanical assistance to surgeons. Currentsurgical navigations systems utilize a vast array of complex sensors andimaging systems in order to aid the surgeon in visualizing the real timerelative position and orientation of an instrument in 3-dimensionalspace. They also act in a generally defined global coordinate systemwhich requires rigorous control of the surgical field in relation tothat global coordinate system. These surgical navigation systemstypically use 3D computer aided tomography and complex imaging functionsto avow the surgeons a re-created vision in real-time of the surgicalsite. Consequently, these systems have extremely high costs to buy andto use (often resulting in institutional ownership such as by thehospital or highly capitalized medical holding groups). Thus, the use ofsurgical navigation is often limited to certain high margin, highexpense and high risk procedures, such as brain or hip replacementsurgery and are typically not used by surgeons focused on extremities orby other surgeons, including for example plastic surgeons, podiatristsand oral surgeons.

Moreover, these surgical navigation systems are typically provided in anoperating arena that includes complex lighting, monitors, biologicalfunction and monitoring systems, and imaging systems and screens such asCT and fluoroscopy systems. While these systems are robustly capable inproviding information to the surgeon, the accompanying surgicaltechnique requires the surgeon to rely almost solely on the imagingscreen and guide placement, while maintaining more than mere peripheralfocus on the actual patient and operating site. This situationconstantly requires the surgeon to refocus his or her attention, leadingto frustration, muscle strain and fatigue. This increases the potentialof complications in the surgery where injury and even loss of life canresult from attendant post-operative troubles.

The problem with these surgical navigation systems, apart from the veryhigh cost, is that the system results in inherent distraction due to thelayout of the displays. In addition, there is a long learning curveassociated with the use of these systems, as well as the cost for theassociated CT/MRI data collection required pre-op which tend to limitthe application of these systems to high grossing procedures. Althoughthese displays and imaging systems represent “cutting edge” surgicalinstrumentation and guidance systems, they increase distraction andstress on surgeons by requiring a greater degree of multi-tasking, andintense focus on multiple locations.

The present invention provides an integration of key advantages of thesesystems into a more “information dense” surgical guidance or “surgicaltargeting” aid, but one which is within the line of sight of the surgeonas well as the procedure's actual location (i.e. within the actual, nota virtual, patient). In large part, this is due to the compact size ofthe guidance system, the use of a localized co-ordinate system, theprovision of the system display in line with the use of the surgicalinstrument and in fact, on the instrument itself, and a graphical userinterface (“GUI”) that is designed to maintain the focus of the surgeonon the location of the instrument and on the work piece as an extensionof the instrument, rather than splitting the surgeon's focus onto adisplaced screen and the surgical instrument, as well as the actual bodyarea of interest.

This invention uses a six or nine degree of freedom (“DOF”) InertialMeasurement Unit (IMU)—to track rotations and accelerations in all threespatial directions by means of using Micro Electrical Mechanical System(MEMS) devices that are cross referenced with a MARG (Magnetic, AngularRate, and Gravity) sensor, so that 3D spatial orientation and motion canbe tracked by converting angular rate to angular position, andacceleration to position through numerical integration. An “LVDT” orlinear potentiometer, measures capacitance or inductance that isproportional to physical position to determine position, which could beutilized in order to measure input distances for the system. Thus, thepresent invention provides a low cost (i.e. having the potential forindividual surgeons to own or even for single use) guidance system,which acts as an aid to surgeons, rather than as a substitute for theirskills and judgment.

SUMMARY OF THE INVENTION

In accordance with the present invention, a surgical targeting guide isprovided which provides a local reference coordinate system defined bythe placement of a linear marker, such as a k-wire, and optionally asimple jig to define the optimal placement points, where the guideenhances the surgeon's ability to remain focused and augments his or herskill in operating as per his or her judgment. The invention allows thesurgeon to place a senor and provide an axis for a reference position.Thus, the marker or pin is used in which two points are used to define arelative 3-D coordinate system. These two points are at a fixed distancewhich are known in 3-D and can be used to identify critical features(i.e. biological landmarks) which allows the surgeon to better locateand hold his or her position without the use of cumbersome or fussy jigsand guides.

The guidance system of the present invention includes a 9 degree offreedom (DOF), three axis accelerometer, gyroscope, and magnetometersensor that could be used to track such motion and orientation (whichhas a typical retail cost between $15 to $40). This sensor, whenintegrated into a system that contains a microcontroller and a visualdisplay, could be rigidly attached to the surgeon's drill or saw toprovide attitude (i.e., orientation relative to a set of defined axes)and positional guidance during surgery. The display could be attached tothe drill or wire guide, or the drill or wire driver, or a cutting tool,such as a saw or burr advantageously with a pattern with a defined entryand exit site. The cutting tool can include electronics and softwareintegrated into the tool with the display through a heads up displaysuch as glasses, and the targeting guide can include safety parametersintegrated into the system. The device can be optimized for specificprocedures, including for example, hip, knee, and spinal surgeries. Thedevice can be modified to provide the visual representation of asimulated anatomy for use or for training, and the device can beoptimized for soft tissue biopsies to minimize the need for CT guidedbiopsies.

In use, a reference axis is defined along with two relative referencepositions, to provide all of the information required to know thedynamics of the system (i.e. surgical instrument orientation andposition relative to the reference position and direction determinedfrom the surgery site.) More specifically, the system needs to define,at minimum, three points that do not lie on the same line in order todetermine a frame of reference. This can be done by either definingthree points in space, two intersecting lines of known length and thepoint of intersection, or a line of known length and two points (one atthe terminal point of the line and one not on the line, where pointsreferring to true positions in a relative reference frame.) Thus, theinvention includes a physical, or a virtual jig or template that can usea reference axis, such as is provided by a guide wire implanted at thesurgical site, and an orthogonal axis is defined by a point on an armplaced at a right angle to the first axis. In a specific embodiment, ajig encircles the guide wire and has a sliding arm which can be extendedalong a bone surface and used to define the optimal location of a pointat a selectively defined distance from the intersection of the axis at aright angle. Means can also be provide to define horizontal, such as alevel bubble, which helps to define the right angle for the second axis.

In order to obtain the real time position, acceleration outputted fromthe accelerometer is mathematically integrated twice. This integrationcan compound bias error and begin to accumulate position drift if theerror signal is not compensated for. Orientation is obtained fromintegrating the time rate change of angular position (angular velocity)once to obtain the real time angular position. From these outputs, thedifference in the initial angular position and reference position can beshown on the display in order to perform the orientation and positionalcorrections needed.

The display of the present invention provides a GUI (graphical userinterface) comprising a spot on a plot (which is advantageously circularor at least two-dimensional such as referential axes or cross-hatching)where the surgeon has the goal of locating the spot in the plot to causethe instrument (such as a drill or screw driver) to act on axis. Asecond GUI displays a relative depth such as by a bar graph (for exampleto locate the distal end of a drill tip or a fastener) so as to providevisual assistance as to the desired amount of penetration.

As a further aspect of the invention, a method of surgery is provided inwhich relates generally to surgery in which a MEMS sensor guidancesystem is mounted on an instrument and in the sight line of the surgeonand which uses the MEMS sensor to determine Inertial Measurement Unitsto track rotation and acceleration in all three spatial directions. Inaccordance with this method, the surgical area is excised to allowaccess to the area for surgical intervention and a reference axis isset, for example by drilling a pilot hole, inserting a k-wire such asalong an axis which a fastener will intersect and defining a referenceaxis by registering two points on the k-wire at a known spaced distance.Next, a loci is defined, for example, an entry point for a fastener; anda depth is determined by measuring a boundary distance for theintervention (e.g., when a fastener will be inserted into a bonesegment, the thickness of the bone is measured which represents thedepth beyond which the surgeon does not wish to penetrate in order toavoid disturbing the soft tissue beyond the cortical surface on the backside of the bone segment). This depth is recorded in a memory of theinstrument in accordance with the invention as a value, dy. Next, avalue is determined along an orthogonal axis, x, which can be determinedusing an actual horizontal jig that includes an indication for afastener entry hole, or a virtual version of the jig which is providedin the microprocessor of the instrument. Then, the instrument includingthe sensor cluster of the invention is placed in relation to the y-axisand x-axis and the device is calibrated using the button marked“calibrate alignment” on this sensor interface display, after assuringthat the axes are properly aligned, for example by checking to be surethat the alignment jig is parallel to the line made with the markedfastener entry location and the centroid axis of the k-wire. The jig canbe provided with a sliding arm to define the second point, and withleveling means to ensure the orientation. Then, with the instrument inplace, the working end is aligned to the area of intervention, forexample, for a drill, the distal end of the drill bit in the drill isaligned to the fastener entry location and the orientation data isdisplayed on the display screen in the GUI as a green circle, and thefastener orientation is determined and maintained by aligning a fastenericon displayed on the instrument sensor duster screen in the properpositioning on the alignment marker and by monitoring the degree of workon the secondary work monitor, for example on a graphical representationof the depth or degree of penetration in the Y-axis. This procedurehelps to ensure the optimal placement for surgical intervention, forexample, for the placement of a pilot hole in order to assure thesubsequent alignment and full seating of a fastener, such as a screwhaving a threaded locking head in relation to a projected internallythreaded locking screw hole in an orthopedic implant. As final steps ofthe method in accordance with the invention, the alignment is repeatedas necessary for the placement of all fasteners, and the surgical accessor incision is dosed. It is also possible to use other means to helpdefine the local coordinate system, such as a beam of light, or other“virtual” templates. Local coordinates can also be obtained frompre-operative CT or MRI scans or intra-operative fluoroscopy. Thetargeting device helps to keep the surgeon's hand “on target”, forexample, through the use of a touchscreen in which measurement inputsare placed to define entry and end points with the use algorithmsinputted to the IC.

The system includes integral or access to memory (for example in amobile device, such as a cell phone) which can be programmed for theplacement of a plurality of fasteners, or with information that can begeneral information for specific procedures, such as angles forosteotomies, or can be information relative to individual patients. Themethod of the present invention is particularly advantageous for use inminimally invasive procedures, and procedures in which fasteners areintroduced percutaneously, or through the skin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is side perspective view of a first representation of thesurgical guide in accordance with a first embodiment of the presentinvention;

FIG. 2 is a detail of the surgical guide of FIG. 1 showing the displayand graphical user interface;

FIG. 3 is a schematic representation of the guidance system inaccordance with the invention illustrating the sensor array, which is incommunication with the microprocessor, which is in reciprocalcommunication with the display;

FIG. 4 is a illustration of a set-up for an orthopedic surgeryillustrating the use of k-wires or pins to define the referencecoordinate system;

FIG. 5 is a radiograph from the front and the back illustrating thereference locations for a set of screws used in the assembly of aconstruct for the repair or fusion of an ankle including a distal fibulaplate and screws and compression screws angled upward through the medialmalleoli into the tibia.

FIG. 6 is a side view illustrating a first distal metatarsal following achevron cut and re-alignment for repair of Hallus Valgus and prior tothe placement of hardware illustrating a step of the method of bunionsurgery in accordance with the present invention;

FIG. 7 is a view following the drilling of a hole and insertion of ak-wire along the axis that a fusion screw will intersect of the methodof bunion surgery of the present invention;

FIG. 8 is an orthographic view of the k-wire in the bone from FIG. 6;

FIG. 9 is an illustration of the location of the fusion screw entrylocation (the smaller dot and the larger dot represents the K-wirelocation);

FIG. 10 illustrates the measurement along the axis of the k-wire of thethickness of the metatarsal, which value is recorded as dy;

FIG. 11 illustrates a tangible alignment jig (which could be replaced bya virtual version of the jig) placed over the k-wire for measurement ofthe marked screw entry point along the length of the alignment jig,which value is recorded as the value dx; and wherein the sensor promptsthe values of dx and dy for entry into the sensor duster interface usingthe display or a remote interface, such as a mobile phone;

FIG. 12 illustrates the placement of a second embodiment of theinstrument in accordance with the invention, in this case, a drill withthe attached sensor duster over the k-wire/alignment jig, and afterassuring that the alignment jig is parallel to the line made with themarked screw entry location and the centroid axis of the k-wire, thesystem is calibrated by pressing the “calibrate alignment” button on thesensor interface;

FIG. 13 illustrates the method of the invention in which the instrumentwith a drill bit hi place is aligned to the screw entry location and inwhich the orientation is displayed on the display screen, in particularby a green circle;

FIG. 14 illustrates the display screen user interface in which theorientation is shown in one GUI, and the depth of work is shown on asecond GUI; and

FIG. 15 illustrates a further embodiment of a jig that can be used tohelp define the local coordinate system of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The guidance system 10 of the present invention as illustrated in FIG. 3provides an integrated sensor duster 12 and integral or separatemicroprocessor 14 including hardware and software that can aid in theproper targeting for example, for fasteners in general or morespecifically for a work piece or a screw, wires or pins, relative to asurgical work area, or for a particular procedure for example forperforming an osteotomy. The guidance system 10 is used with a surgicalinstrument 20, and can be provided separately for attachment to theinstrument, or can be bunt into the instrument. Alternatively, as isconvenient, it can be provided as components, such as the display whichcan be integrated into various surgical tools, or into a separatedisplay, such as glasses or even a mobile device. Since the system isused in surgery, it needs to be able to be sterile so that it can beprovided sterile as a sterilized disposable device for a single use,which is attached to a re-usable instrument or it could also besterilizable, in which case, it could be integrated into the instrument.

The guidance system 10 has a senor duster or sensor array 12 thatincludes at least (and possibly only) a 9 degree of freedom (DOF) threeaxis accelerometer 32, gyroscope 34, and magnetometer 36 sensor thatcould be used to track such motion and orientation. This sensor duster12 is further integrated into a system that contains a microcontroller38 and a visual display 40 (preferably both integrated into a singleunit, but where the microcontroller 38 or display 40 could be accessedremotely by the senor duster, including, for example, on a mobiledevice, such as a cell phone). The required capabilities of themicroprocessor are comparable to the capabilities of the Arduino Mega2560 microcontroller with a ATmega 2560 microprocessor with 256 KB flashmemory, 8 KB of SRAM, 4 KB EEPROM, and a docking speed of 16 Mhz. Thus,the guidance system is advantageously integrated into or attached to thesurgeon's instrument, 20 such as a drill or saw to provide feedback tothe surgeon with respect to orientation relative to a defined axis (i.e.“attitude”) as well as positional guidance (meaning the ability of thesystem to direct the surgeon to maintain a desired position duringsurgery. The guidance system 10 defines a reference 100 along with arelative reference position 102, to provide the information required toknow the dynamics of the system (i.e. surgical instrument orientationand position relative to the reference position and direction determinedfrom the surgery site.) In order to obtain the real time position, themicroprocessor 38 uses the data from the acceleration and mathematicallyintegrates it twice. Since this integration can compound bias error andbegin to accumulate position drift, the error signal is compensated forusing a defined offset or a specific algorithm in a software componentof the invention. Orientation is obtained from integrating the time ratechange of angular position (angular velocity) once to obtain the realtime angular position and these outputs, the difference in the initialangular position and reference special position can be shown on thedisplay 40 in order to allow the surgeon to perform the orientation andpositional corrections needed In order to match the directional outputof the GUI 42 on the display 40 of the guidance system 10.

The display 40 of the present invention provides a GUI 42 (graphicaluser interface) which for example, includes a targeting or guidancemechanism 46 such as a spot 47 on a plot 48 (which is advantageouslycircular) where the surgeon has the goal of centering the spot 47 in theplot 48 to cause the instrument (10 such as a drill or screw driver) towork on axis 104 relative to the defined reference 100. A second GUIprovides a bar graph 110, which displays a relative depth (for examplefor the distal end of a drill tip or a fastener) to provide visualassistance as to the desired amount of penetration of the drill bit orfastener.

As an alternative to, or in addition to the display, the guidance systemcan include an audio alert system, for example, a series of beeps orbuzzing that can either increase or decrease volume, temp of frequencyin order to present information to the guidance user, for example byincreasing the tempo as the work piece comes to it's desired location.In addition, the guidance system can include safety means, such as stopsto avoid drilling too deep or in the wrong location.

in further embodiment, the mechanical jig 210 that is illustrated inFIG. 15 has an opening or bore 212 which captures a guide wire to definea first axis extending along the axis of the opening 212 and defined bythe interior side walls of the opening. A first arm 214 extends at afirst right angle to the opening, and includes a level, such as thebubble level 216 to ensure that the jig is level. An orthogonal slidingarm 218 is provided and is provided with hatch marks to provide a visualindication of a defined length along the second arm 218. Optionally arm214 can be provided with a mechanism for translating the arm along theaxis of arm 218 without changing the angle between the two arms in orderto provide an optimal geometry for associated sensors, such as linearpotentionmeters. The jig is provided with one, two or more 100 mm 10kOhm linear potentiometers 220, and is connected, such as by a wired 222or a wireless connection to the microprocessor of the system. Ideally,the potentiometers are located on different arms of the jig to verifythe relative location of the coordinate system, and the k-wire may alsoinclude a potentiometer (i.e. a third one) here to mark that distance aswell. The jig may include an offset from the bone to accommodate theanatomy as desired.

As a further aspect of the invention, a method of surgery is providedwhich relates generally to surgery in which a MEMS sensor guidancesystem 10 is mounted on an instrument 20 and with uses the MEMS sensor12 to determine Inertial Measurement Units to track rotation andacceleration in all three spatial directions. One such method of surgeryis illustrated as a chevron cut bunionectomy, although it is understoodthat it can be used for other surgeries, for example, for fusion such asfor the placement of a compression screw, or for any small or long boneor spinal or maxofacial surgery, for example using a plate or implantthat is fixed relative to a bone or bones, by a fastener, such as ascrew, or many other surgical procedures.

In accordance with this method, the surgical area is prepped, such asfor example by excision to allow access to the area for surgicalintervention (or in the case of minimally invasive surgery to avow animplant to be placed without a fully opened incision). Next, a referenceaxis is set, for example by drilling a pilot hole, in the bone 310(having a chevron incision 311) and inserting a k-wire 312 such as alongan axis which a fastener will intersect and defining a reference axis byregistering two points on the k-wire at a known spaced distance, in thememory of the microprocessor. Next, a loci is defined, for example, anentry point 314 for a fastener 316; and a depth is determined bymeasuring a boundary distance for the intervention (e.g., when afastener will be inserted into a bone segment, the thickness of the boneis measured which represents the depth beyond which the surgeon does notwish to penetrate in order to avoid disturbing the soft tissue beyondthe cortical surface on the back side of the bone segment). This depthis recorded in a memory of the microprocessor of the instrument inaccordance with the invention as a value, dy. Next, a value isdetermined along an orthogonal axis, x, which can be determined using anactual horizontal jig 318 that includes an indication for a fastenerentry hole, or by a virtual version of the jig for example utilizing areflected light beam instead of the metal jig and wherein the virtualjig is provided in the microprocessor of the instrument. Then, theinstrument preferably including the sensor cluster of the invention isplaced in relation to the y-axis and x-axis and the device is calibratedusing the button marked “calibrate alignment” on this sensor interfacedisplay, after assuring that the axes are properly aligned, for exampleby checking to be sure that the alignment jig is parallel to the linemade with the marked fastener entry location and the centroid axis ofthe k-wire. Then, with the instrument in place, the working end isaligned to the area of intervention, for example, for a drill, thedistal end of the drill bit in the drill is aligned to the fastenerentry location and the orientation data is displayed on the displayscreen such as by a green circle, and the fastener orientation isdetermined and maintained by aligning a fastener icon displayed on theinstrument sensor cluster screen in the proper positioning on thealignment marker and by monitoring the degree of work on the secondarywork monitor, for example on a graphical representation of the depth ordegree of penetration in the Y-axis. This procedure helps to ensure theoptimal placement for surgical intervention, for example, for theplacement of a pilot hole in order to assure the subsequent alignmentand full seating of a fastener, such as a screw having a threadedlocking head in relation to a projected internally threaded lockingscrew hole in an orthopedic implant. As final steps of the method inaccordance with the invention, the alignment is repeated as necessaryfor the placement of all fasteners, and the surgical access or incisionis closed.

The method of the present invention is particularly advantageous for usein minimally invasive procedures, and procedures in which fasteners areintroduced percutaneously, or through the skin.

In accordance with the present invention, various procedures can beperformed with the assistance of the instrument guidance system,including for example, inserting fasteners including with up-loadedspecific information as to the relative location of a plurality offasteners or of the relative location of bone fragments for typicalfracture patterns, or in the case of reconstruction, the angle ofincision for example by maneuvering the desired axis over time, sincethe present system has the advantage of allowing a rate change oforientation to be monitored. Likewise, the device can be used to accesspatient specific information, which might be gathered on the basis ofpre-surgical imaging including for example, fluoroscopy, MRI, tomographyand x-ray imaging.

While in accordance with the patent statutes the best mode and preferredembodiment have been set forth, the scope of the invention is notlimited thereto, but rather by the scope of the attached claims.

What is claimed is:
 1. A surgical guidance system for use with a workpiece in a surgical field and comprising a MEMS sensor and amicroprocessor having memory loaded with software that enables theinterpretation of real-time data gathered by the MEMS sensor wherein theMEMS sensor tracks the orientation and movement over time of the workpiece in the surgical field using a locally defined coordinate system.2. A surgical guidance system as set forth in claim I further comprisinga display or audio command mechanism.
 3. A surgical guidance system asset forth in claim 2 wherein the display displays one or multiplegraphical user interfaces.
 4. A surgical guidance system as set forth inclaim 3 wherein the graphical user interface recommends an orientationor vector of the work piece over time.
 5. A surgical guidance system asset forth in claim 4 wherein the graphical user interface includes a twodimensional matrix and a marker responding to the location of the workpiece over time, and the graphical user interface recommends theorientation through the display by tracking the marker on the twodimensional matrix and indicating a desirable location of the markercorresponding to a desirable location of the work piece.
 6. A surgicalguidance system as set forth in claim 5 wherein the two dimensionalmatrix is a circle, square, or rectangle and the marker is a spot.
 7. Asurgical guidance system as set forth in claim 1 wherein the graphicaluser interface can be used to guide a change in orientation of the workpiece.
 8. A surgical guidance system as set forth in claim 7 wherein thework piece is used for cutting and the change of orientation of the workpiece dictates an angle of cuffing.
 9. A surgical guidance system as setforth in claim 1 including a display where the display includesgraphical user interface which indicates the depth of the work pieceover time.
 10. A surgical guidance system as set forth in claim 9wherein the graphical user interface is a bar graph which acts as asurgical depth guide.
 12. A surgical guidance system as set forth inclaim 10 wherein the graphical user interface further includes a twodimensional matrix with a marker.
 13. A surgical guidance system as setforth in claim 1 wherein the system includes a memory including data asto the desired location of multiple fasteners and the memory records alocal coordinate system which is determined by a user during surgery.14. A surgical guidance system as set forth in claim 13 wherein thememory includes information as to the anatomy of a specific patient. 15.A surgical guidance system as set forth in claim 13 wherein the memoryincludes information as to the anatomy of a specific surgical procedure.16. A surgical instrument comprising an instrument having a work pieceand an integrated surgical guidance system which tracks the work piecein a surgical field and the surgical guidance system comprising a MEMSsensor which is carried on the instrument and a microprocessor havingmemory loaded with software that enables the interpretation of real-timedata gathered by the MEMS sensor wherein the MEMS sensor tracks theorientation and movement over time of the work piece in the surgicalfield using a locally defined coordinate system.
 17. A surgicalinstrument as set forth in claim 16 wherein the sensor is a six or ninedegree of freedom sensor.
 18. A surgical instrument as set forth inclaim 16 wherein the work piece is one of a screw driver, a blade, aburr or an ablation piece.
 19. A surgical instrument as set forth inclaim 18 further including a display having a graphical user interfacewhich recommends an orientation of the work piece over time.
 20. Asurgical guidance system as set forth in claim 9 wherein the display ismounted to one or more of a guide, a driver and a cutting tool.
 21. Asurgical guidance system as set forth in claim 9 wherein the display ismounted to a cutting tool and the cutting tool includes a template witha defined entry or exit site.
 22. A surgical guidance system as setforth in claim 1 wherein the system includes one or more safetyparameters.
 23. A surgical guidance system as set forth in claim 1wherein the system is optimized for a specific surgical procedure.
 24. Asurgical guidance system as set forth in claim 23 wherein the surgicalprocedure is a spinal surgery.
 25. A surgical guidance system as setforth in claim 1 wherein the system includes a simulated visualrepresentation of a simulated anatomy.
 26. A surgical guidance system asset forth in claim 1 further comprising one or more linearpotentiometer.
 27. A surgical instrument as set forth in claim 16further comprising one or more linear potentiometer.